diff --git a/README.md b/README.md
index 524d0235c7..2e29f9b497 100644
--- a/README.md
+++ b/README.md
@@ -45,8 +45,8 @@ compromises backward compatibility.
  * Release mode produces heavily optimized code. What other projects call
    "Link Time Optimization" Zig does automatically.
  * Mark functions as tests and automatically run them with `zig test`.
- * Currently supported architectures: `x86_64`, `i386`
- * Currently supported operating systems: linux, macosx
+ * Currently supported architectures: `x86_64`
+ * Currently supported operating systems: linux
  * Friendly toward package maintainers. Reproducible build, bootstrapping
    process carefully documented. Issues filed by package maintainers are
    considered especially important.
@@ -103,7 +103,7 @@ cd build
 cmake .. -DCMAKE_INSTALL_PREFIX=$(pwd) -DZIG_LIBC_LIB_DIR=$(dirname $(cc -print-file-name=crt1.o)) -DZIG_LIBC_INCLUDE_DIR=$(echo -n | cc -E -x c - -v 2>&1 | grep -B1 "End of search list." | head -n1 | cut -c 2- | sed "s/ .*//") -DZIG_LIBC_STATIC_LIB_DIR=$(dirname $(cc -print-file-name=crtbegin.o))
 make
 make install
-./run_tests
+./zig build --build-file ../build.zig test
 ```
 
 ### Release / Install Build
diff --git a/build.zig b/build.zig
index 918a629cf6..378ea66c86 100644
--- a/build.zig
+++ b/build.zig
@@ -5,44 +5,19 @@ pub fn build(b: &Builder) {
     const test_filter = b.option([]const u8, "test-filter", "Skip tests that do not match filter");
     const test_step = b.step("test", "Run all the tests");
 
-    const behavior_tests = b.step("test-behavior", "Run the behavior tests");
-    test_step.dependOn(behavior_tests);
-    for ([]bool{false, true}) |release| {
-        for ([]bool{false, true}) |link_libc| {
-            const these_tests = b.addTest("test/behavior.zig");
-            these_tests.setNamePrefix(b.fmt("behavior-{}-{} ",
-                if (release) "release" else "debug",
-                if (link_libc) "c" else "bare"));
-            these_tests.setFilter(test_filter);
-            these_tests.setRelease(release);
-            if (link_libc) {
-                these_tests.linkLibrary("c");
-            }
-            behavior_tests.dependOn(&these_tests.step);
-        }
-    }
+    const cleanup = b.addRemoveDirTree("test_artifacts");
+    test_step.dependOn(&cleanup.step);
 
-    const std_lib_tests = b.step("test-std", "Run the standard library tests");
-    test_step.dependOn(std_lib_tests);
-    for ([]bool{false, true}) |release| {
-        for ([]bool{false, true}) |link_libc| {
-            const these_tests = b.addTest("std/index.zig");
-            these_tests.setNamePrefix(b.fmt("std-{}-{} ",
-                if (release) "release" else "debug",
-                if (link_libc) "c" else "bare"));
-            these_tests.setFilter(test_filter);
-            these_tests.setRelease(release);
-            if (link_libc) {
-                these_tests.linkLibrary("c");
-            }
-            std_lib_tests.dependOn(&these_tests.step);
-        }
-    }
+    cleanup.step.dependOn(tests.addPkgTests(b, test_filter,
+        "test/behavior.zig", "behavior", "Run the behavior tests"));
 
-    test_step.dependOn(tests.addCompareOutputTests(b, test_filter));
-    test_step.dependOn(tests.addBuildExampleTests(b, test_filter));
-    test_step.dependOn(tests.addCompileErrorTests(b, test_filter));
-    test_step.dependOn(tests.addAssembleAndLinkTests(b, test_filter));
-    test_step.dependOn(tests.addDebugSafetyTests(b, test_filter));
-    test_step.dependOn(tests.addParseHTests(b, test_filter));
+    cleanup.step.dependOn(tests.addPkgTests(b, test_filter,
+        "std/index.zig", "std", "Run the standard library tests"));
+
+    cleanup.step.dependOn(tests.addCompareOutputTests(b, test_filter));
+    cleanup.step.dependOn(tests.addBuildExampleTests(b, test_filter));
+    cleanup.step.dependOn(tests.addCompileErrorTests(b, test_filter));
+    cleanup.step.dependOn(tests.addAssembleAndLinkTests(b, test_filter));
+    cleanup.step.dependOn(tests.addDebugSafetyTests(b, test_filter));
+    cleanup.step.dependOn(tests.addParseHTests(b, test_filter));
 }
diff --git a/std/build.zig b/std/build.zig
index 20fb4cad5c..d22d6b660a 100644
--- a/std/build.zig
+++ b/std/build.zig
@@ -195,6 +195,12 @@ pub const Builder = struct {
         return log_step;
     }
 
+    pub fn addRemoveDirTree(self: &Builder, dir_path: []const u8) -> &RemoveDirStep {
+        const remove_dir_step = %%self.allocator.create(RemoveDirStep);
+        *remove_dir_step = RemoveDirStep.init(self, dir_path);
+        return remove_dir_step;
+    }
+
     pub fn version(self: &const Builder, major: u32, minor: u32, patch: u32) -> Version {
         Version {
             .major = major,
@@ -1548,10 +1554,12 @@ pub const WriteFileStep = struct {
         const full_path = self.builder.pathFromRoot(self.file_path);
         const full_path_dir = %%os.path.dirname(self.builder.allocator, full_path);
         os.makePath(self.builder.allocator, full_path_dir) %% |err| {
-            debug.panic("unable to make path {}: {}\n", full_path_dir, @errorName(err));
+            %%io.stderr.printf("unable to make path {}: {}\n", full_path_dir, @errorName(err));
+            return err;
         };
         io.writeFile(full_path, self.data, self.builder.allocator) %% |err| {
-            debug.panic("unable to write {}: {}\n", full_path, @errorName(err));
+            %%io.stderr.printf("unable to write {}: {}\n", full_path, @errorName(err));
+            return err;
         };
     }
 };
@@ -1576,6 +1584,30 @@ pub const LogStep = struct {
     }
 };
 
+pub const RemoveDirStep = struct {
+    step: Step,
+    builder: &Builder,
+    dir_path: []const u8,
+
+    pub fn init(builder: &Builder, dir_path: []const u8) -> RemoveDirStep {
+        return RemoveDirStep {
+            .builder = builder,
+            .step = Step.init(builder.fmt("RemoveDir {}", dir_path), builder.allocator, make),
+            .dir_path = dir_path,
+        };
+    }
+
+    fn make(step: &Step) -> %void {
+        const self = @fieldParentPtr(RemoveDirStep, "step", step);
+
+        const full_path = self.builder.pathFromRoot(self.dir_path);
+        os.deleteTree(self.builder.allocator, full_path) %% |err| {
+            %%io.stderr.printf("Unable to remove {}: {}\n", full_path, @errorName(err));
+            return err;
+        };
+    }
+};
+
 pub const Step = struct {
     name: []const u8,
     makeFn: fn(self: &Step) -> %void,
diff --git a/std/io.zig b/std/io.zig
index 03960867b5..e9c70d9611 100644
--- a/std/io.zig
+++ b/std/io.zig
@@ -57,8 +57,6 @@ error NoMem;
 error Unseekable;
 error Eof;
 
-const buffer_size = 4 * 1024;
-
 pub const OpenRead     = 0b0001;
 pub const OpenWrite    = 0b0010;
 pub const OpenCreate   = 0b0100;
@@ -66,7 +64,7 @@ pub const OpenTruncate = 0b1000;
 
 pub const OutStream = struct {
     fd: i32,
-    buffer: [buffer_size]u8,
+    buffer: [os.page_size]u8,
     index: usize,
 
     /// `path` may need to be copied in memory to add a null terminating byte. In this case
@@ -97,7 +95,7 @@ pub const OutStream = struct {
     }
 
     pub fn write(self: &OutStream, bytes: []const u8) -> %void {
-        if (bytes.len >= buffer_size) {
+        if (bytes.len >= self.buffer.len) {
             %return self.flush();
             return os.posixWrite(self.fd, bytes);
         }
@@ -329,7 +327,7 @@ pub const InStream = struct {
     }
 
     pub fn readAll(is: &InStream, buf: &Buffer0) -> %void {
-        %return buf.resize(buffer_size);
+        %return buf.resize(os.page_size);
 
         var actual_buf_len: usize = 0;
         while (true) {
@@ -341,7 +339,7 @@ pub const InStream = struct {
                 return buf.resize(actual_buf_len);
             }
 
-            %return buf.resize(actual_buf_len + buffer_size);
+            %return buf.resize(actual_buf_len + os.page_size);
         }
     }
 };
diff --git a/std/list.zig b/std/list.zig
index d01e3a88a4..b20cd06fef 100644
--- a/std/list.zig
+++ b/std/list.zig
@@ -61,10 +61,15 @@ pub fn List(comptime T: type) -> type{
             l.len = new_length;
             return result;
         }
+
+        pub fn pop(self: &Self) -> T {
+            self.len -= 1;
+            return self.items[self.len];
+        }
     }
 }
 
-test "basicListTest" {
+test "basic list test" {
     var list = List(i32).init(&debug.global_allocator);
     defer list.deinit();
 
@@ -75,4 +80,7 @@ test "basicListTest" {
     {var i: usize = 0; while (i < 10; i += 1) {
         assert(list.items[i] == i32(i + 1));
     }}
+
+    assert(list.pop() == 10);
+    assert(list.len == 9);
 }
diff --git a/std/mem.zig b/std/mem.zig
index 66e119b503..6a2d854fc7 100644
--- a/std/mem.zig
+++ b/std/mem.zig
@@ -9,6 +9,8 @@ error NoMem;
 
 pub const Allocator = struct {
     allocFn: fn (self: &Allocator, n: usize) -> %[]u8,
+    /// Note that old_mem may be a slice of length 0, in which case reallocFn
+    /// should simply call allocFn
     reallocFn: fn (self: &Allocator, old_mem: []u8, new_size: usize) -> %[]u8,
     freeFn: fn (self: &Allocator, mem: []u8),
 
diff --git a/std/os/index.zig b/std/os/index.zig
index 7da623d3ce..0113706796 100644
--- a/std/os/index.zig
+++ b/std/os/index.zig
@@ -17,6 +17,8 @@ pub const line_sep = switch (@compileVar("os")) {
     else => "\n",
 };
 
+pub const page_size = 4 * 1024;
+
 const debug = @import("../debug.zig");
 const assert = debug.assert;
 
@@ -32,6 +34,7 @@ const cstr = @import("../cstr.zig");
 
 const io = @import("../io.zig");
 const base64 = @import("../base64.zig");
+const List = @import("../list.zig").List;
 
 error Unexpected;
 error SystemResources;
@@ -46,6 +49,7 @@ error SymLinkLoop;
 error ReadOnlyFileSystem;
 error LinkQuotaExceeded;
 error RenameAcrossMountPoints;
+error DirNotEmpty;
 
 /// Fills `buf` with random bytes. If linking against libc, this calls the
 /// appropriate OS-specific library call. Otherwise it uses the zig standard
@@ -585,3 +589,177 @@ pub fn makePath(allocator: &Allocator, full_path: []const u8) -> %void {
         // TODO stat the file and return an error if it's not a directory
     };
 }
+
+/// Returns ::error.DirNotEmpty if the directory is not empty.
+/// To delete a directory recursively, see ::deleteTree
+pub fn deleteDir(allocator: &Allocator, dir_path: []const u8) -> %void {
+    const path_buf = %return allocator.alloc(u8, dir_path.len + 1);
+    defer allocator.free(path_buf);
+
+    mem.copy(u8, path_buf, dir_path);
+    path_buf[dir_path.len] = 0;
+
+    const err = posix.getErrno(posix.rmdir(path_buf.ptr));
+    if (err > 0) {
+        return switch (err) {
+            errno.EACCES, errno.EPERM => error.AccessDenied,
+            errno.EBUSY => error.FileBusy,
+            errno.EFAULT, errno.EINVAL => unreachable,
+            errno.ELOOP => error.SymLinkLoop,
+            errno.ENAMETOOLONG => error.NameTooLong,
+            errno.ENOENT => error.FileNotFound,
+            errno.ENOMEM => error.SystemResources,
+            errno.ENOTDIR => error.NotDir,
+            errno.EEXIST, errno.ENOTEMPTY => error.DirNotEmpty,
+            errno.EROFS => error.ReadOnlyFileSystem,
+            else => error.Unexpected,
+        };
+    }
+}
+
+/// Whether ::full_path describes a symlink, file, or directory, this function
+/// removes it. If it cannot be removed because it is a non-empty directory,
+/// this function recursively removes its entries and then tries again.
+// TODO non-recursive implementation
+pub fn deleteTree(allocator: &Allocator, full_path: []const u8) -> %void {
+start_over:
+    // First, try deleting the item as a file. This way we don't follow sym links.
+    try (deleteFile(allocator, full_path)) {
+        return;
+    } else |err| {
+        if (err == error.FileNotFound)
+            return;
+        if (err != error.IsDir)
+            return err;
+    }
+    {
+        var dir = Dir.open(allocator, full_path) %% |err| {
+            if (err == error.FileNotFound)
+                return;
+            if (err == error.NotDir)
+                goto start_over;
+            return err;
+        };
+        defer dir.close();
+
+        var full_entry_buf = List(u8).init(allocator);
+        defer full_entry_buf.deinit();
+
+        while (true) {
+            const entry = (%return dir.next()) ?? break;
+
+            %return full_entry_buf.resize(full_path.len + entry.name.len + 1);
+            const full_entry_path = full_entry_buf.toSlice();
+            mem.copy(u8, full_entry_path, full_path);
+            full_entry_path[full_path.len] = '/';
+            mem.copy(u8, full_entry_path[full_path.len + 1...], entry.name);
+
+            %return deleteTree(allocator, full_entry_path);
+        }
+    }
+    return deleteDir(allocator, full_path);
+}
+
+pub const Dir = struct {
+    fd: i32,
+    allocator: &Allocator,
+    buf: []u8,
+    index: usize,
+    end_index: usize,
+
+    const LinuxEntry = extern struct {
+        d_ino: usize,
+        d_off: usize,
+        d_reclen: u16,
+        d_name: u8, // field address is the address of first byte of name
+    };
+
+    pub const Entry = struct {
+        name: []const u8,
+        kind: Kind,
+
+        pub const Kind = enum {
+            BlockDevice,
+            CharacterDevice,
+            Directory,
+            NamedPipe,
+            SymLink,
+            File,
+            UnixDomainSocket,
+            Unknown,
+        };
+    };
+
+    pub fn open(allocator: &Allocator, dir_path: []const u8) -> %Dir {
+        const fd = %return posixOpen(dir_path, posix.O_RDONLY|posix.O_DIRECTORY|posix.O_CLOEXEC, 0, allocator);
+        return Dir {
+            .allocator = allocator,
+            .fd = fd,
+            .index = 0,
+            .end_index = 0,
+            .buf = []u8{},
+        };
+    }
+
+    pub fn close(self: &Dir) {
+        self.allocator.free(self.buf);
+        posixClose(self.fd);
+    }
+
+    /// Memory such as file names referenced in this returned entry becomes invalid
+    /// with subsequent calls to next, as well as when this ::Dir is deinitialized.
+    pub fn next(self: &Dir) -> %?Entry {
+    start_over:
+        if (self.index >= self.end_index) {
+            if (self.buf.len == 0) {
+                self.buf = %return self.allocator.alloc(u8, 2); //page_size);
+            }
+
+            while (true) {
+                const result = posix.getdents(self.fd, self.buf.ptr, self.buf.len);
+                const err = linux.getErrno(result);
+                if (err > 0) {
+                    switch (err) {
+                        errno.EBADF, errno.EFAULT, errno.ENOTDIR => unreachable,
+                        errno.EINVAL => {
+                            self.buf = %return self.allocator.realloc(u8, self.buf, self.buf.len * 2);
+                            continue;
+                        },
+                        else => return error.Unexpected,
+                    };
+                }
+                if (result == 0)
+                    return null;
+                self.index = 0;
+                self.end_index = result;
+                break;
+            }
+        }
+        const linux_entry = @ptrcast(&LinuxEntry, &self.buf[self.index]);
+        const next_index = self.index + linux_entry.d_reclen;
+        self.index = next_index;
+
+        const name = (&linux_entry.d_name)[0...cstr.len(&linux_entry.d_name)];
+
+        // skip . and .. entries
+        if (mem.eql(u8, name, ".") or mem.eql(u8, name, "..")) {
+            goto start_over;
+        }
+
+        const type_char = self.buf[next_index - 1];
+        const entry_kind = switch (type_char) {
+            posix.DT_BLK => Entry.Kind.BlockDevice,
+            posix.DT_CHR => Entry.Kind.CharacterDevice,
+            posix.DT_DIR => Entry.Kind.Directory,
+            posix.DT_FIFO => Entry.Kind.NamedPipe,
+            posix.DT_LNK => Entry.Kind.SymLink,
+            posix.DT_REG => Entry.Kind.File,
+            posix.DT_SOCK => Entry.Kind.UnixDomainSocket,
+            else => Entry.Kind.Unknown,
+        };
+        return Entry {
+            .name = name,
+            .kind = entry_kind,
+        };
+    }
+};
diff --git a/std/os/linux.zig b/std/os/linux.zig
index 7c841fafad..1ebade3baf 100644
--- a/std/os/linux.zig
+++ b/std/os/linux.zig
@@ -241,6 +241,15 @@ pub const AF_NFC = PF_NFC;
 pub const AF_VSOCK = PF_VSOCK;
 pub const AF_MAX = PF_MAX;
 
+pub const DT_UNKNOWN = 0;
+pub const DT_FIFO = 1;
+pub const DT_CHR = 2;
+pub const DT_DIR = 4;
+pub const DT_BLK = 6;
+pub const DT_REG = 8;
+pub const DT_LNK = 10;
+pub const DT_SOCK = 12;
+pub const DT_WHT = 14;
 
 fn unsigned(s: i32) -> u32 { *@ptrcast(&u32, &s) }
 fn signed(s: u32) -> i32 { *@ptrcast(&i32, &s) }
@@ -273,6 +282,10 @@ pub fn getcwd(buf: &u8, size: usize) -> usize {
     arch.syscall2(arch.SYS_getcwd, usize(buf), size)
 }
 
+pub fn getdents(fd: i32, dirp: &u8, count: usize) -> usize {
+    arch.syscall3(arch.SYS_getdents, usize(fd), usize(dirp), usize(count))
+}
+
 pub fn mkdir(path: &const u8, mode: usize) -> usize {
     arch.syscall2(arch.SYS_mkdir, usize(path), mode)
 }
@@ -291,6 +304,10 @@ pub fn read(fd: i32, buf: &u8, count: usize) -> usize {
     arch.syscall3(arch.SYS_read, usize(fd), usize(buf), count)
 }
 
+pub fn rmdir(path: &const u8) -> usize {
+    arch.syscall1(arch.SYS_rmdir, usize(path))
+}
+
 pub fn symlink(existing: &const u8, new: &const u8) -> usize {
     arch.syscall2(arch.SYS_symlink, usize(existing), usize(new))
 }
diff --git a/test/tests.zig b/test/tests.zig
index 88e2231304..d760856339 100644
--- a/test/tests.zig
+++ b/test/tests.zig
@@ -103,6 +103,27 @@ pub fn addParseHTests(b: &build.Builder, test_filter: ?[]const u8) -> &build.Ste
     return cases.step;
 }
 
+pub fn addPkgTests(b: &build.Builder, test_filter: ?[]const u8, root_src: []const u8,
+    name:[] const u8, desc: []const u8) -> &build.Step
+{
+    const step = b.step(b.fmt("test-{}", name), desc);
+    for ([]bool{false, true}) |release| {
+        for ([]bool{false, true}) |link_libc| {
+            const these_tests = b.addTest(root_src);
+            these_tests.setNamePrefix(b.fmt("{}-{}-{} ", name,
+                if (release) "release" else "debug",
+                if (link_libc) "c" else "bare"));
+            these_tests.setFilter(test_filter);
+            these_tests.setRelease(release);
+            if (link_libc) {
+                these_tests.linkLibrary("c");
+            }
+            step.dependOn(&these_tests.step);
+        }
+    }
+    return step;
+}
+
 pub const CompareOutputContext = struct {
     b: &build.Builder,
     step: &build.Step,